1. Field of the Invention
In recent years, vehicles (hereinafter, collectively referred to as plug-in vehicles) such as electric cars or plug-in hybrid cars that can be charged by the use of an external power supply have been increasingly put to practical use. A dedicated charging cable having a control unit called a CCID (Charge Circuit Interrupt Device) is used to connect a plug-in vehicle to an external power supply.
The standard on an interface between the charging cable and the plug-in vehicle is defined by the “SAE (Electric Vehicle Conductive Charge Coupler) standard” of the U.S. or the “General Requirements for Electric Vehicle Conductive Charging System (the Japanese Electric Vehicle Standard)” of Japan. The charging sequence of a plug-in vehicle defined in the standard is substantially as follows.
First, a CCID of a charging cable transmits a control pilot signal (hereinafter, abbreviated as a pilot signal) to a charging-control ECU (Electronic Control Unit) mounted on a plug-in vehicle and determines that the charging cable is connected to the plug-in vehicle when the voltage of the pilot signal is changed from an initial value V1 (for example, 12 V) to V2 (for example, 9 V).
Then, the CCID of the charging cable informs the ECU of the plug-in vehicle of the rated current of a power supply facility by transmitting a pilot signal with a duty ratio corresponding to the rated current of the power supply facility (including an external power supply and a charging cable).
Subsequently, the ECU of the plug-in vehicle informs the CCID of the charging cable of completion of the preparation for charging by changing the voltage of the pilot signal from V2 to V3 (for example, 6 V).
Then, when detecting that the voltage of the pilot signal has changed from V2 to V3, the CCID of the charging cable determines that the preparation for charging of the plug-in vehicle side is completed, and turns on a relay used to supply the power of the external power supply to the plug-in vehicle (that is, starts the supply of power).
In this way, the pilot signal is a signal essential for controlling the charging of the plug-in vehicle and it is very important to detect abnormality of the pilot signal. For example, Japanese Unexamined Patent Application, First Publication No. 2009-71989 discloses a technique of detecting a disconnection of a control line used for transmission of a pilot signal in a state where a plug-in vehicle is connected to an external power supply via a charging cable.
2. Description of the Related Art
As described in Japanese Unexamined Patent Application, First Publication No. 2009-71989, the pilot signal is input to a CPU (Central Processing Unit) via an input buffer in an ECU of the plug-in vehicle. Since a recommended input voltage range is determined for the input buffer but the voltage of the pilot signal varies in a broad range, the input buffer may not work normally or the input buffer may be destroyed in a worst case. Accordingly, a circuit for protecting the input buffer is necessary, but such a circuit is not disclosed in Japanese Unexamined Patent Application, First Publication No. 2009-71989.
The invention is made in consideration of the above-mentioned circumstances and an object thereof is to provide an electronic control unit that can protect an input buffer for a pilot signal, which a pilot signal is input to, disposed in a stage preceding a processor such as a CPU when a plug-in vehicle is charged from an external power supply via a charging cable.